Field of the Invention
The present invention relates to an apparatus for measuring birefringence and retardation values of various film materials, and more particularly, it relates to a measuring apparatus which can obtain dispersion of retardation values with respect to wavelengths of measuring light.
Description of the Background Art
In a conventional retardation measuring apparatus, a sample to be measured is held between a polarizer and an analyzer which are maintained in a constant relation of polarization directions such as a parallel nicol relation, for example. Then monochromatic light is applied through the sample from the polarizer to measure intensity of the light being passed through the sample and transmitted through the analyzer, while relatively rotating the polarizer and the analyzer, maintained in the constant relation. Thus measured is dependency of the transmitted light intensity on the angle of rotation, thereby obtaining the retardation value with respect to the measuring light of the current wavelength.
In the conventional measuring apparatus, the sample or the combination of the polarizer and the analyzer is thus rotated in order to observe angle dependency of the transmitted light intensity. Therefore, it takes minutes to collect data required for obtaining a retardation value on a single point of the sample. Further, obtained through single measurement is only a retardation value at a specific wavelength as selected. In order to obtain a retardation value at another wavelength, it is necessary to change the wavelength of the measuring light as well as to newly rotate the sample or the combination of the polarizer and the analyzer again for collecting angle dependency data of the transmitted light intensity. Thus, a considerably long time is required also for collecting data for obtaining retardation values at a few wavelengths. Due to such a problem, data collection at a large number of wavelengths for obtaining dispersion of retardation values with respect to the wavelengths requires a great effort.